Along with the improvements in the integration degrees of semiconductor devices, such as semiconductor integrated circuits (LSI), and improvements in the recording densities of hard disks, formations of fine patterns are currently desired. It is desirable to establish a microprocessing technique corresponding to the formation of such fine pattern, and in the technical field of photolithography, pattern forming techniques using electron beam exposure have been studied.
The pattern formation technique using electron beam exposure relatively easily enables the formation of fine pattern in the size of 0.1 μm or smaller, which cannot be formed by ultraviolet ray exposure. Therefore, this technique is regarded as the pattern formation technique of the next generation, and as having a bright prospect. However, in the pattern formation technique using electron beam exposure, the exposure duration is long due to the wiring system originated in the nature of electron beams, and as a result, the throughput thereof is low.
To solve this problem, it is desirable to improve the throughput by improving the sensitivity of an electron beam resist, thereby reducing the exposure duration.
As the method for improving the sensitivity of the electron beam resist, there has been known the method in which an electron scattering layer formed of a material having a large electron scattering coefficient (e.g. a single metal such as Pt, and Mo) is formed below the film formed of the electron resist (for example, see Japanese Patent Application Laid-Open (JP-A) No. 58-105140).
In this method, the larger number of the scattered electrons is stayed in the area adjacent to the incident area of the electron beam as the electron scattering increases in the electron scattering layer, and the scattered electrons located in such area are used for photoactivity of the electron beam resist. Therefore, the sensitivity of the electron beam resist improves. In this method, however, the process for forming the electron scattering layer below the electron beam resist, and the process for selectively removing the electron scattering layer after forming a pattern on a base are both complicated.
Moreover, the relationship between high sensitivity and high resolution is a relationship of trade-off in the electron beam resist. For example, as an amount of an acid generator increases in the electron beam resist, the sensitivity of the electron beam resist film increases, but resolution of the electron beam resist film decreases.
Moreover, as a unique problem for electron beam exposure, there is an adverse influence from forward scattering (scattering in the resist film at the time of incident of an electron beam) and back scattering of electrons (scattering in the resist due to reflection from the inner portion of the base). The scattering degree of electron beams depends on the atomic weight of the element to receive an impact. Therefore, if a heavy element (e.g. a semiconductor wiring) is present below the pattern forming part, the back scattering increases, which improves the apparent sensitivity improves. Namely, in the case where there is a pattern containing the heavy element at the bottom thereof, it is difficult to form a resist pattern at a constant size.
For the reasons mentioned above, developments of materials and process techniques for improving a sensitivity of an electron resist without impairing a resolution of the electron resist have been strongly desired.